Butterfly pen knife



FIG. 1 is a top plan view of the butterfly pen knife showing my new design;

FIG. 2 is a side elevational view thereof;

FIG. 3 is an opposite side elevational view thereof;

FIG. 4 is a bottom plan view thereof;

FIG. 5 is an end elevational view thereof;

FIG. 6 is an opposite end elevational view thereof;

FIG. 7 is a top plan view thereof with the blade shown in the closed position;

FIG. 8 is a perspective view thereof with the blade shown in the closed position. 

The ornamental design for a butterfly pen knife, as shown and described. 